Fuel burning heating systems in general use today frequently consist of a burner that is supplied with air for combustion from a motor-powered fan or blower assembly. Typically, the air suppliers for heating system burners may be radial airflow devices driven by conventional electric motors taking power from commercial electrical supply lines. In the United States, commercial electrical power is supplied typically at 110 and 220 volts at 60 cycles, and in many foreign countries electrical power is supplied typically at 220 volts at 50 cycles, and such electric power supplies operate the electric motors driving the air suppliers at speeds on the order of 2500 to 3500 rpm. At such low speeds, the size of the motor driven blower is large in order to supply the amount of air required for combustion of the fuel.
One type of blower which is commonly used is called a Sirocco blower in which air is drawn into the center of a cylindrical, cage-like air-moving wheel by its rotation and is forced radially outwardly from the center by curved vanes that extend along the axis of rotation at the cylindrical periphery of the air-moving wheel. A scroll-like casing surrounds the cylindrical periphery of the air-moving wheel to collect the air outflow and direct it tangentially through a peripheral outlet for delivery to the fuel burning chambers of a furnace. Operating at speeds of 2500 to 3500 rpm Sirocco blowers are large in size in order to deliver a sufficient air for fuel combustion in most heating systems. In addition, due to their poor aerodynamic shape, the efficiency of such blowers can be as low as 10 to 15 percent.